Optical data communications technology has a number of advantages over wire technology, such as increased bandwidth, data rate and response characteristics superior to those of conventional wire technology. Also, optical technology is essentially immune to radio frequency interference (RFI) and electromagnetic interference (EMI) issues associated with wire technology. Optical data communication is therefore desirable in a variety of applications such as multi-chip modules (MCMs), printed circuit board (PCB) technologies, and integrated backplanes.
In conventional optical connectors, electronic circuitry, optical source and optical detectors are typically mounted on PCBs which are received in card guides mounted to an equipment frame. A backplane mounted to the rear of the frame includes board edge connectors aligned with the card guides and electrical conductors interconnecting the board edge connectors. The circuit boards are provided with board edge electrical contacts which are received in the board edge connectors when the circuit boards are inserted in the card guides to electrically connect the circuitry to the electrical conductors on the back plane. The electrical conductors provide the required electrical connections between circuit boards.
The circuit boards also include optical connector parts which are optically coupled to the optical sources and to the optical detectors of the receivers and transmitters. The board mounted optical connector parts must be mated with frame mounted optical connector parts to optically connect the optical sources and the optical detectors to optical fibers terminating on the frame mounted optical connectors. The optical fibers are typically a glass fiber manufactured from glass.
In the current board edge optical connector arrangements the circuit board mounted optical connector parts are mounted at leading edges of the circuit boards. One disadvantage of this arrangement is that the leading edges are already congested with board edge electrical contacts. In addition, in the board edge optical connector arrangements the frame mounted optical connector parts are mounted at the back plane, which is already congested with electrical board edge connectors and electrical conductors. In current systems, optical fibers may be left to hang loose between packs or bundles of fibers which tend to create a messy (“rat's nest”) entanglement of fibers. Further, what is needed is a method to reorder the layers within an optical cable without increasing its thickness (or bulkiness), without twisting or bending the waveguide layers, and without using optical vias.
Another approach is to use polymer waveguide optical backplanes, which can contain thousands of optical channels. A polymer waveguide may be composed of two different polymer materials, for instance, a lower index cladding material and a higher index core material. Light is guided in a core (optical channels) due to the index contrast between the core and clad regions. The optical backplane may interconnect multiple server drawers, distributing and reordering the optical channels between the drawers as necessary. To facilitate the reordering within a multi-layer optical cable, it is necessary to reorder the individual waveguide layers from the input connector to the output connector. The waveguide layer reordering may be achieved by twisting and bending individual waveguide layers. This approach can result in excessive cable bulk. Further, current waveguides are difficult to bend to achieve cable reordering of the optical fibers between two connection points. Another approach is to introduce optical vias between waveguide layers to facilitate the layer redistribution, however, optical vias introduce additional loss and are costly to fabricate. Another difficult and undesirable approach is to bend (or twist) layers to realize layer reordering.
In view of the shortcoming in the prior art, there is a need to provide an apparatus and method to connect large numbers of optical fibers to an optical backplane and avoid the entanglement of wires associated with multiple fiber-to-fiber connections and/or routing systems. Additionally, there is a need for a device and/or method of reordering the layers within an optical cable without increasing its thickness (or bulkiness), without twisting or bending the waveguide layers, and without using optical vias.
Referring to FIGS. 1-2, a prior art optical cable 10 includes four waveguides 14. Each of the waveguides 14 includes a plurality of optical fibers 22 (shown in FIG. 3) encased in a polymer such that the waveguide 14 is planar and has a defined width. Each of the waveguides 14 and optical fibers 22 have a first and a second end connected to respective first and second connectors 30, 32. Each of the first and second connectors 30, 32 include connector holes in columns and rows, or connection points, i.e., for receiving optical fibers, which may also include, for example, electrically conductive sleeves, pins, or other connection points. Each of the ends of the waveguides, i.e., the optical fiber 22 ends, correspond to waveguide connection points, collectively designated as connection points 31, 33, respectively, on the first and second connectors 30, 32. Each of the first ends of the optical fibers 22 of the waveguides 14 are connecting to columns and rows of the first connector, and each of the second ends of the optical fibers 22 of the waveguides are connected to corresponding columns and rows of the second connector. Each of the ends of the optical fibers 22 of each of the waveguides 14 are connected to specified waveguide connection points 31, 33 on each of the first and second connectors 30, 32 resulting in a connection pattern (alternatively called a pin pattern) on the first and second connectors 30, 32. The connection pattern is a geometric pattern, for example, as shown in the connectors 30, 32 of FIG. 2, which depicts a rectangular grid of connection points 31, 33 arranged in waveguide fiber columns 1-4 and rows 5a-5l, as shown in greater detail in the generic connector 75 in FIG. 5. Waveguide fiber connection points in column 1 are the outermost column on both connectors 30, 31. Rows 5a-5l, which are grouped as rows 5, form the rectangular grid of connection points 31, 33 with the columns on each of the connectors 30, 32. Each of the first and second connectors 30, 32, include four connector columns 8a, 8b, 8c, 8d, as shown in generic connector 75 in FIG. 5, from outside to inside, as shown in a generic connector 75 having connectors holes 78, shown in FIG. 5. The connection holes 78 form a connection hole pattern in one or more connectors which is identical, and is generally a grid pattern as shown in FIGS. 5 and 7.
The connector 75 of FIG. 5 is equivalent to, in the orientation of the related figures, the left side connector, for example, connectors 30, 60, 130, and its mirror image applies to the right side connectors 32, 64, 140 of the figures. However, the optical fiber column, i.e., the optical fibers at one end of each of the waveguides which correspond to the optical fibers at the other end of each of the waveguides, may be positioned in a different connector column in the opposite connector. Thus, as shown in FIG. 3, and discussed more extensively below, fiber column 1 on the first connector, corresponding to fiber column 1 on the second connector, may be physically located at a different connector column on each of the connectors 30, 31.
As shown in FIG. 2, the connection point pattern of the first connector 30 geometrically corresponds to the connection point pattern of the second connector 32. Further, the optical fiber connection pattern, i.e., the waveguide connection points 31, 33, geometrically correspond between the first and second connectors. Specifically, the first end of the same optical fiber of the same waveguide is connected to a connection point of the first connector 30 located at connector column 1, row 5a of the first connector, and the second end of the same optical fiber is connected to a connection point of the second connector 32 located at connector column 1, row 5a of the second connector, wherein the connectors have the same geometric connector pattern (or pin pattern). Thus, each optical fiber at one end of the wave guide 14 is connected to a corresponding row on the opposite connector, which also is the same physical location on the connector for each of the connectors 30, 32. Any reordering of the waveguide optical fibers is difficult due to the semi-rigid nature of the waveguides, and individual reordering of each of the optical fibers is difficult and tedious.
Referring to FIGS. 3 and 4, an alternative prior art optical cable 50 includes a wave guide 54 having optical fibers 22 connected from a first connector 60 to a second connector 64, as shown in FIG. 3. As shown in FIG. 4, first connector 60 has a different fibber connection point geometry than the second connector 64. Specifically, the second connector 64 has a fiber connection point 66 fiber column sequence of 2, 1, 4, 3, from outside to inside, opposed to the first connector 60 having a fiber connection point 62 fiber column sequence of 1, 2, 3, 4. Thus, the second connector 64 does not have the same waveguide fiber connection column geometry as the first connector 60. In the optical cable 50 shown in FIG. 3, an optical fiber 22 is shown individually connected at one end to connector column 1 on the first connector 60, and to connector column 1 on the second connector 64. As can be seen, the optical fiber in fiber row 1 of the first connector 60, corresponds to connector hole row 8a, and fiber row 1 is shifted to connector hole row 8b in the second connector 64. As shown in FIG. 4, on the second connector 64, fiber column 1, at physical location connector column 8b, corresponds to fiber column 1 on the first connector 60, at physical location connector column 8a. This is because, for example, one end of the optical fibers 22 (thereby one end of a waveguide) are connected to connection points at connector column 8a of the first connector 60, thereby being designated as fiber column 1, and the other end of the same optical fibers 22 (thereby the opposite end of the waveguide) are connected to connection points at column 8b on the second connector 64, which is designated as fiber column 1 for the second connector 64, which is physically shifted over one column, that is connector column 8b, from outside to inside of the second connector 64. Therefore, the fiber 22 connected at column 1 on the first connector 60, is connected to column 1 on the second connector 64, however, column 1 on the second connector 64 is physically located where column 2 is on the first connector 60.